Problem: $-10lm + 10ln - l - 10 = -3m - 9$ Solve for $l$.
Explanation: Combine constant terms on the right. $-10lm + 10ln - l - {10} = -3m - {9}$ $-10lm + 10ln - l = -3m + {1}$ Notice that all the terms on the left-hand side of the equation have $l$ in them. $-10{l}m + 10{l}n - 1{l} = -3m + 1$ Factor out the $l$ ${l} \cdot \left( -10m + 10n - 1 \right) = -3m + 1$ Isolate the $l$ $l \cdot \left( -{10m + 10n - 1} \right) = -3m + 1$ $l = \dfrac{ -3m + 1 }{ -{10m + 10n - 1} }$ We can simplify this by multiplying the top and bottom by $-1$. $l= \dfrac{3m - 1}{10m - 10n + 1}$